1. Field of the Invention
The present invention relates to an optical disc apparatus, and more specifically, to a method for using an optical disc apparatus to extract information recorded in a BCA (burst cutting area) or NBCA (narrow burst cutting area, or non-burst cutting area) on a surface of an optical disc.
2. Description of the Prior Art
A BCA is an area arranged on the inner periphery of an optical disc. A BCA-Code, which is a series of low reflectance stripes, is formed in the BCA. The BCA is formed on a disc using a laser cutting process after the fabrication of the disc. Thus, the manufacturer can record desired information, in the form of the BCA-Code, on the disc. For example, the serial number of the disc or anti-counterfeit information can be recorded to the disc. Similar to the BCA, the NBCA also performs the same function as the BCA and stores data in the same format.
Different Digital Versatile Disc (DVD) formats now take advantage of the BCA and NBCA for protecting content stored on the DVD. Specifically, the DVD-RAM format uses the BCA, and the DVD-R and DVD-RW formats both use the NBCA to store information. If content in the DVD-RAM, DVD-R, and DVD-RW formats is to be protected, each will use the Content Protection for Recordable Media (CPRM) to protect the data. The DVD-RAM format will store data in the BCA format for utilizing CPRM, and the DVD-R and DVD-RW formats will store data in the NBCA format for utilizing CPRM. A different protection standard called Content Protection for Prerecorded Media (CPPM) is used for the DVD-ROM format. The DVD-ROM may contain BCA-Code, but no BCA-Code information is needed for utilizing CPPM. As will be shown below, the data structures for BCA-Code and NBCA-Code are identical, so the following description will be limited to the BCA for simplicity.
Typically, information including a sync byte and resync bytes are recorded on the BCA of a disc. The sync byte is adapted to indicate the start point of the BCA. Only one sync byte exists in the entire portion of the BCA. Each of the sync byte and resync bytes includes a fixed sync pattern and a sync code.
Please refer to FIG. 1. FIG. 1 is a block diagram illustrating an optical disc drive 100 according to the prior art. Information recorded on the surface of an optical disc 110 is reproduced by an optical pickup 114. The optical pickup 114 optically picks up the information recorded on a data recording surface of the optical disc 110 rotating in accordance with a drive force from the spindle motor 112 and then converts the picked-up information into an electrical signal, namely, a radio frequency (RF) signal.
The RF signal from the optical pickup 114 is applied to an RF amplifier unit 120. The optical pickup 114 moves radially between the inner and outer peripheries of the surface of the optical disc 110 in accordance with a drive force from a feeding motor 126. The RF amplifier unit 120 amplifies the RF signal from the optical pickup 114, and removes noise and distortion from the amplified signal through a waveform equalization circuit, thereby outputting a shaped RF signal. The shaped RF signal from the RF amplifier unit 120 is sent to an envelope detector and slicing unit 142, which transforms the RF signal from the BCA to a digitized signal BCA_RZ (BCA return-to-zero). The BCA_RZ signal is then sent to a BCA-Code processing unit 150 for extracting BCA-Code channel bits from the BCA_RZ signal and for performing sync and resync detection. This data is then sent to a BCA-Code decoding unit 144. The BCA-Code decoding unit 144 removes sync and resync bytes for extracting the data stored in the BCA-Code, performs phase encoded (PE) demodulation on the data, and performs an EDC or ECC check of the data contained in the BCA-Code. A DECODE_OK flag is sent to a microprocessor 140 for indicating the decoding status. Then, the data stored in the BCA-Code is stored in a dynamic random access memory (DRAM) 146.
A spindle motor control unit 128 controls rotation of the spindle motor 112. The spindle motor control unit 128 can operate under constant angular velocity (CAV) mode if the spindle motor 112 provides a feedback signal Fg to the spindle motor control unit 128, as will be explained below. If the feedback signal Fg is not provided to the spindle motor control unit 128, the spindle motor control unit 128 can operate under open loop mode by “kicking” the spindle motor 112 with a constant force when reading BCA-Code. The RF amplifier unit 120 also sends signals for focus and tracking servos, that is, a focus error signal FE and a tracking error signal TE, to a servo digital signal processor (DSP) 122. The servo DSP 122 applies control signals to a servo driving unit 124 for controlling a focus servo and a tracking servo, based on the focus error signal FE and tracking error signal TE, respectively. The servo driving unit 124 generates the drive voltages required to move the optical pickup 114, as well as to drive the tracking and focus servos, and applies the respective drive voltages to the optical pickup 114 and feeding motor 126, where the servos are located.
Please refer to FIG. 2. FIG. 2 is a diagram showing an example of a BCA_RZ signal train. BCA-Code information is stored in a series of channel bits, each representing a digital “1” or “0”. Period T, shown from time t2 to t3, represents a time width of one channel bit. In the BCA_RZ (BCA return-to-zero) format, channel bits representing a digital “1” have an initial value of “1” that returns to “0” before the end of a period of that bit. For example, at time t1, the BCA_RZ signal has a leading edge with a value of “1” that returns to “0” before the channel bit period ends at time t2. For channel bits representing a digital “0”, the BCA_RZ signal remains at “0” for the entire duration of the period of that bit. This is shown in channel bits ranging from time t2 to t3 and also from time t3 to t4. Therefore, FIG. 2 represents a BCA-Code of (1,0,0,1,0,0,0,1,1,0,1).
According to the specification of the BCA, T can be expressed in terms of a fixed clock CLKh that has a frequency Fh (in MHz) according to Eqn.1,                     T        =                              8.89            *            Fh                    r                                    (        1        )            where r represents a rotation speed multiplier such as 2, 4, 8, etc, where the rotation speed is calculated as 24*r Hz, and where T is a time expressed in cycles of CLKh.
As can be seen in FIG. 2 from time t4 to t8, Tpp represents a time width between succeeding leading edges of the BCA_RZ signal. Also according to the BCA specification, Tpp can be expressed according to Eqn.2,                     Tpp        =                                            (                                                8.89                  ⁢                  n                                ±                2                            )                        *            Fh                    r                                    (        2        )            where n is an integer with a value of 1, 2, 3, or 4, and where Tpp is also a time expressed in cycles of CLKh.
The integer n represents the number of channel bit widths between succeeding leading edges of the BCA_RZ signal. For example, from t1 to t4, n would have a value of 3, from t4 to t8, n would have a value of 4, from t8 to t9, n would have a value of 1, and from t9 to t11, n would have a value of 2.
Based on Eqn.2, a new quantity Tppmax is used to describe a maximum value of Tpp throughout the BCA_RZ signal train, as expressed according to Eqn.3,                                           33.56            *            Fh                    r                ≤        Tppmax        ≤                              37.56            *            Fh                    r                                    (        3        )            wherein Tppmax is a time expressed in cycles of CLKh.
The formula shown in Eqn.3 is derived from Eqn.2 by setting n=4 and subtracting and adding the value of 2. As will be shown below, n can never be larger than 4, so the value of Tppmax is computed with n=4.
Please refer to FIG. 3 to FIG. 6. FIG. 3 and FIG. 4 illustrate tables of a recorded information state of the BCA. Recorded on the BCA are a sync byte, resync bytes, and a variety of information. The sync byte is denoted by SBBCA whereas each resync byte is denoted by RSBCA followed by a number from 1 to 15. FIG. 3 illustrates the configuration of the BCA. As shown, each piece of information recorded on the BCA is denoted by I, and C denotes an ECC parity. In FIG. 4, data structures of the sync byte and resync bytes, each of which consists of a fixed sync pattern and a sync code, are illustrated. In FIG. 3, the BCA has blocks each consisting of 16 information bytes designated as I. The BCA may have a maximum of 13 blocks. Each block of the BCA includes sub-blocks each containing 4 bytes of information. Every sub-block follows a resync byte. Accordingly, one information block consists of 4 resync bytes and 16 information bytes.
The sync byte is the first sync information indicative of the start position of the BCA. Accordingly, only one sync byte exists in the BCA. On the other hand, the resync byte is the second sync information adapted to provide a synchronization for 4 information bytes, for example, I0, I1, I2, and I3. As shown in FIG. 4, such a resync byte consists of a fixed sync pattern having a size of 8 channel bits and a sync code having a size of 4 data bits. The 8 channel bits are recorded with RZ (return-to-zero) modulation and the 4 data bits are recorded with PE-RZ (phase encoded return-to-zero) modulation, and actually contain two bits for every bit shown in FIG. 4. The fixed sync pattern is a particular pattern which is configured not to be detected from the general information area, but to be detected only from the sync and resync area. The sync code of each resync byte is a serial number allocated to an associated information block and adapted to distinguish the information block from other information blocks.
As shown in FIG. 4, the fixed pattern for channel bits is the same for the sync byte and resync bytes. In each of these sync and resync bytes, a (1,0,0,0,1) pattern is shown. Therefore, a period Tpp can be obtained from the sync and resync bytes in which the period between two successive leading edges would use the case of n=4, as seen in Eqn.2.
FIG. 5 and FIG. 6 illustrate tables of a recorded information state of the NBCA. Please note that the data structures for the BCA and the NBCA are identical, as shown in FIG. 3 to FIG. 6. Since the BCA and the NBCA have identical data structures, no further explanation will be given for the NBCA data structure.